Food-dependent regurgitate effectiveness in the defence of grasshoppers against ants: the case of bracken-fed Abracris flavolineata (Orthoptera: Acrididae)

The deterrence of a grasshopper, Abracris flavolineata, regurgitate against the fire ant, Solenopsis geminata, depends on diet. The ant deterrence of oral discharges of bracken-fed insects is greater than for those feeding on lettuce. A water extract of Pteridium caudatum fronds is also more potent in deterring the ants than a lettuce extract. A positive correlation between the content of phenolics in the regurgitate and deterrence is observed and bracken-derived oral fluids contain a 4.6-fold higher content of phenolics than lettuce-derived material. Nevertheless, no statistical difference is observed in condensed tannins content. The rate of transformation of bracken phenolics in the digestive tract of A. flavolineata proceeds quickly because, after only 48 h of discontinuing the diet, 53% of phenolics and 94% of tannins relative to the total present in the fronds are no longer in the ejected digestive fluid. It is suggested that this reduction may be a mechanism by which one fraction of the phenolics is metabolized or excreted and the other is used as defence via the oral secretion. The powerful deterrence index of bracken water extract indicates that other active secondary metabolites may also be present.